Recovery of methyl amine



Patented Sept. 6, `1932 ,f UNITED STATES PATE-NT OFFicEg A LLOYD C.SWALLENAND BENJAMIN C. EOECEELER, OE TERRE HAUTE, II\1i IANi i,-AsAvsIGNoRs To COMMERCIAL sOLvENTs CORPORATION, OE TERRE HAUTE, INDIANA,

f cyanic acid.y bv tlieaction of ammonia on ACORIORATION or MARYLAND f yv RECOVERY OF METHYL AMINE Application med Augen 2i, i930. sefiai No.476,794.

This invention relates to a method for the recovery of methyl amine frommixtures containing ammonia. More specifically, this invention relatesto a process for the recovery of methyl amine from the `mixturesobtained in the catalytic synthesis from methanol and ammonia.

Methyl vamine may be prepared from for-V maldehyde and ammoniumchloride, from methyl cyanate, bythe reduction of hydromethyl iodide,methyl chloride, methyl niti'ate, etc. However, it may best .be madeupon a commercial scale by catalytic synthesis. from methanol andammonia, as disclosed in co-pending applications Serial Nos. 4cs,992ant1468-993, filed July is, i930, by

Lloyd C. Swallen and Jerome Martin. In

Y this method, methanol vapor and ammonia are passed over metallic oxidedehydrating catalysts or over aluminium silicate attemperatures of from300O to'500" C. The mixture leaving the catalyst is found to comprisemethyl amine (a mixture of mono di-and tri-methyl amines), ammonia, anyunconverted methanol, the water which is formed in the reaction, and anydecomposition products of the methanol or ammonia, such as hydrogen andcarbon monoxide. e

The recovery of methyl amine from such ammonia-containing mixtures haspresented a problem which has not been satisfactorilyv solved until thepresent time. Expensive and complicated methods involving the formationof the salts and fractional crystallization or selective solution havebeen employed. These methods, however, are obviouslydisadvantageous fromthe standpoint of commercial production. y

The present invention comprises a satisfactory and economical method forthe separation `of-methyl amine from ammonia. By methyl amine is meantthe mono, di-,.tri, or any mixtureof these. However,the monomethyl amineis of primary importance at the present time from a commercialstandpoint,` and the present method is devised Vto recover a mixturecontaining substantially all of the mono-compound. It has beenfoundthatthe physical properties of ammonia differ sufficiently from those ofmethyl amine to make possible their virtually complete separation byfractional distillation.

y Although the present process is especially i `applicable to themixtures resulting from the catalytic synthesis from methanolV andainmonia, it isto be distinctly understood that the invention is nott'obe limited to the use edto any mixtures of methyl amine and ammonia.`For example, if methyl amine 1s `produced by the reaction of methylchloride and ammonia. the baseswill be present as the hydrochloric acidsalts; these, however, may,l

be freedk `by treatment with a non-volatile base, and the resulting`mixture, which contains methyl amine and aii'imonia, treated by "themethod of the present invention.

`This invention consists essentially in liquefying the mixture of methylamine and ammonia, and separating them "by fractional distillation. Themethod for carrying out the process may best be seen from theaccompanying flow sheet. It is seen `that the mixture leaving thecatalystis first cooled in `order to remove the unconverted methanol,

the Water formed in the reaction, and any `condensation products orother products of side reactions which maybe removed at this point by`condensation.' The uncondensed gases are then compressed in the firststage of a two-stage compressonto a pressure of about 'condensable gasesare bled off. These gases consist ot' hydrogen. carbon monoxide,nitrogen, and other decomposition yproducts of the materials enteringthe catalystA chamber. The liouid amines andammonia arefed `directlyfrom the crude storage tank A,into approximately the middle of thecolumn ofa pressure still. The recovered ammonia.,

The mixture then f of such mixtures; The'proces's may be adaptioo whichcomes 0H at the top of the column is condensed and sent to storagetanks, to be used in the catalysis. rl'he amines reflux in the columnand are collected in the kettle, from which they may be removedcontinuouslyor semi-continuously and sent to mixing tanks where they arediluted to the desired concentration for storage, shipping,

ctc. As may be seen from the flow sheet, the'y condensates containingWater, methanol, etc., are collected and distilled to recover any aminesor ammonia, and then fractionated to recover any methanol, etc. Thewater from this distillation is used to scrub the noncondensable gasesand is then returned to the still. i f' The .distillation is carried outat approximately 150 lbs. and suflicient heat is supplied to the kettleto give a good reflux in the column and a steady distillation oftheammonia Without mechanically carrying over the f amine. The followingexample will best SeWe to illustrate the method ot carrying out thedistillation. The liquefied ammonia and amine, obtained Ifrom thecatalytic product as described above, are fed into a thirty-platebubble-cap column-just above the fourteenth plate. The still comprises asteani-jacleted pressure kettle, `and the condenser is a horizontaldouble-pipe cooler fitted with a b vpass back to thetop of thecolumn.Heat is supplied to the kettle and the liquefied gases are introducedinto the column at a pressure of approximately 150 lbs. In normaloperation, a portion of the condensate is run to the recovered ammoniastorage tank, and the A remainder is liv-passed back to the top of tlecolumn to give a reflux. ratio of about 5:1. lVheri operating underthese conditions. the distillate is found'to` consist of about 95%ammonia, `0.5% mono-methyl amine, and 4.5% of higher amines, mainlytri-ii'iethyl. By this method of operation the ammonia content of themixture of amines remaining in the kettle may be reduced to less than 2mol% of thetotal amines.

It is to be understood` of course, that this invention is not to belimited to the use of the particular equipment described above, nor tothe particular operating conditions. For example, a packedcolumn mightbe used inplace of the bubble-cap plate type, and a dephlegmator mightbe employed in series with the. condenser instead ot by-passing a partot the total condensate back to the column. lVhile 150 lbs. is thepreferred pressure at which theoperation is to be carried out, thepressure may be varied Widely Without departing from the spirit ottheinvention. It.l has been found `that a range of 125 to 200 lbs. issatisfactory, but even these values are not limiting. The lower limit otpressure will depend upon the available cooling means for .thecondensers; the higher limit upon the cost ofequipment, andthemaintenance cost for thesisof methyl amine `the pressure is notsuiiiciently high to necessitate very expensive equipment.

If desired, the process may be opei'atcd by the batch method instead ofcontinuously or semicontinuously. i

The invention now' having been described,

what is claimed is:

vl. A process for recovering methyl amine from mixtures containingammonia, which comprises liqueying the methyl amine and ammonia andfractionally distilling under` pressure to separate the ammonia from themethyl amine.

2. from mixtures containing ammonia, which comprises liquefying themethyl amine and ammonia and fractionally distilling un'der pressure offrom 125 to 200 lbs. to-separate the ammonia from the methyl amine. f

3. A process for recovering methyl amine from mixtures containingammonia,r\vhich comprises liquefying tlie methyl amine and ammonia andfractionally distillingunder a pressure of about 150 lbs. to separatethe ammonia from the methyl amine.

,4. A process for recovering methyl amine from mixtures 'containingammonia, which comprises removing by condensation the products ivhichare liquid at atmospheric temperatures and pressures,. liquetying themethyl amine and ammonia, bleeding otffthe non-condeiisable gases, andfractionally distilling under pressure to separate the 'ainmonia fromthe/methyl amine.

f `5. A process for recovering methyl amine from mixtures containingammonia, which comprises removing by condensation the products which areliquid at atmospheric temperatures and pressures, liquefying the methylamine and ammonia, bleeding otf the iion-condensable gases, andfractioiiallydis-` tilling under pressures of from 125 vto 200 lbs.

toA Separate the ammonia from the methyl amine. l

6. A process for recovering methyl vamine from mixtures containingammonial which methyl amine and ammonia, bleeding 0H the non-condensablegases, and fractionally distilling under a pressure of about 150 lbs. toseparatethe ammonia from the methyl amine. 7. A process for recoveringmethyl amine from mixtures obtained in the catalytic synfrom methanoland ammonia, wvhich comprises liquetying the methylv amine and ammoniaand fractionally distilling under vpressure to separate the ainmoniafrom the methyl amine. f

8. A process for recovering methyl amine A process for recovering methylamine' from mixtures obtained in the catalytic synthesis of methyl aminefrom methanol and ammonia, which comprises liquefying the methyl amineand ammoniav and fractionally distilling under pressures of from 125 to200 lbs. to separate the ammonia from the methyl amine.

9. A process for recovering methyl amine from mixtures obtained in thecatalytic synthesis of methyl amine from methanol and ammonia, whichcomprises liquefying the methyl amine and ammonia and fractionally .Idistilling under a pressure of about 150 lbs.

10. A process for recoveringmethyl amine from mixtures obtained inthecatalytic synthesis of methyl amine from methanol and ammonia, whichcomprises removing by condensation the products which are liquid atatmospheric temperatures and pressures, liquefying the methyl amine andammonia, bleeding off the non-eondensable gases, and fractionally distilling under pressure to sep- :irate the ammonia from the methylamine.

11. A process for recovering methyl amine from mixtures obtained in thecatalytic synthesis of methyl amine from methanol and ammonia, whichcomprises removing by condensation the products which are liquid atatmospheric temperatures and pressures,

liquefying themethyl amine and ammonia,v

bleeding ofi' the non-condensable gases, and fractionally distilling`under pressures of from 125 to 200 lbs. to separate the ammonia from themethyl amine.

12. A process for recovering methyl amine from mixtures obtained in thecatalytic synthesis of methyl amine from methanol and ammonia whichcomprises removing by condensation the products which are liquid atatmospheric temperatures and pressures, liquefying the methyl amine andammonia,

bleeding oi the non-condensable gases, and" fractionallyy distillingunder a pressure of about lbs. v

In testimony whereof we aiix our signatures.

LLOYD C. SWALLEN. B. CLARK BOECKELER.

